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Introductory field skills-33742 > Rock classification for fieldwork > Flashcards

Rock classification for fieldwork Flashcards

1
Q

What 3 broad categories of rock are there?

A

igneous
sedimentary
metamorphic

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2
Q

What di crystalline rocks grow together to form?

A

aggregates of crystals

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3
Q

What type of rock are crystalline rocks generally?

A

igneous or metamorphic

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4
Q

Will crystalline rocks typically be more compacted or fragmented?

A

compacted

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5
Q

What are fragmental rocks like?

A

minerals and rock particles that have been transported and deposited together by water, wind or ice

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6
Q

What the the general characteristics of fragmental rocks?

A

Often rounded
Friable
Mostly sedimentary

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7
Q

What does it mean when saying a rock if friable?

A

tends to break up

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8
Q

How are igneous rocks formed?

A

cooling of magma

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9
Q

How will the crystals typically be orientated in igneous deposits?

A

randomly unless from lava flow then will have flow orientatation

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10
Q

What are sedimentary rocks formed from?

A

rock formed from sediment (solid material) moved to current position by water (less so but ice and wind)

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11
Q

What might the solid material that makes up sedimentary rocks be?

A

other rock fragments,
mineral fragments
organic material
Precipitate minerals

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12
Q

What are the general characteristics of sedimentary rocks?

A

Friable
fossil
rounded fragment pre-existing rock

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13
Q

What is sedimentary bedding?

A

planar structure reflecting the sediment being ‘laid down’ in ‘beds’

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14
Q

What conditions are regional metamorphic rocks formed under?

A

High pressure ad high temperature

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15
Q

How will platy minerals grow with their orientation? (regional metamorphism)

A

Mica and clay etc. have preferred direction orientation right angle to principle pressure

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16
Q

What does it mean saying regional metamorphism creates foliation banding?

A

when pressure produces alignment and may produce strong cleavage

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17
Q

What will other metamorphic rocks be like?

Not regional metamorphic rocks

A

Either don’t contain platey minerals hence no
foliation
Metamorphosed just by heat with minimal pressure (no foliation)

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18
Q

What 2 broad catagories can igneous rocks be classified by?

A

Extrusive
Intrusive

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19
Q

What are extrusive minerals like?

A

Fast cooling - limited crystal growth
Found cose to surface

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20
Q

What will mineral formation be like for extrusive igneous rocks?

A

Medium to slow cooling
Medium to large crystal growth

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21
Q

How can a more accurate nme be given to igneous rocks in the field?

A

Crystal size
Colour (proportion light to dark)

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22
Q

What will the different coarse (>5mm) crystal igenous rocks be at dark, intermediate and light?

A

Dark- gabbro
Intermediate (50/50)- diorite or granodiorite
Light- granodiorite or granite

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23
Q

What will the different medium (1-5mm) crystal igenous rocks be at dark, intermediate and light?

A

Dark- dolerite
Intermediate- microdiorite
Light- microgranite

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24
Q

What will the different fine (1mm) crystal igenous rocks be at dark, intermediate and light?

A

Dark- basalt
Intermediate- andesite
Light- rhyolite

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25
Q

What parameters can be used to define igneous rocks to a greater detail?

A

Mode of formation-Intrusive/extrusive
Percentage composition
Grain/crystal size
Texture
Colour
Density

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26
Q

What other name can be given to other metamorphic rocks?

A

contact metamorphism (as will tend to form around igneous intrusion)

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27
Q

What will the lithology and pressure/temp be for a rock with this property: Fine grained, but hard, very fissile along strong cleavage?

A

Slate
Low temp & pressure

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28
Q

What will the lithology and pressure/temp be for a rock with this property: Fine-medium grained, hard, surface may have a slight sheen due to growth of micaceous minerals?

A

Phyllite
Greater pressure and temp than slate

29
Q

What will the lithology and pressure/temp be for a rock with this property: Coarser grained with obvious mica crystals, still shows good cleavage?

A

Schist
Greater temp and pressure than phyllite

30
Q

What will the lithology and pressure/temp be for a rock with this property: Coarse grained with no cleavage, but distinct bands of light and dark minerals?

A

Gneiss
High temp and pressure

31
Q

What will the lithology of the other metamorphic rocks be with these properties: Dominated by one mineral – quartz. Crystalline, hard rock. Pale grey to buff coloured?

A

Quartzite

32
Q

What will the lithology of the other metamorphic rocks be with these properties: Dominated by one mineral – calcite. Crystalline but softer than quartzite?

A

Marble

33
Q

What will the lithology of the other metamorphic rocks be with these properties: Fine grained rock, may see original sedimentary bedding. Rock fractures irregularly across the bedding planes, not
along it?

A

Hornfels

34
Q

What are the three main types of sedimentary rock?

A

Siliclastic rock
Carbonates
other non-clastic rocks

35
Q

what are siliclastic rocks made up of?

A

fragments of pre-exixting rock material

36
Q

What are carbinate rocks made up of?

A

clastic or precipitated from solution

37
Q

What will the lithology of a very coarse (>4mm) sedimentry rock by? (classfication)

A

conglomerate (rounded fragments)
breccia (angular fragments)

38
Q

What will the lithology of a coarse (2-4mm) sedimentry rock by? (classfication)

A

granulstone (gritstone)

39
Q

What will the lithology of a medium (0.006-2mm) sedimentry rock by? (classfication)

A

arenites (sandstones)

40
Q

What will the lithology of a fine (<0.006mm) sedimentry rock by? (classfication)

A

mudrocks

41
Q

What fractions can mudrocks be splt into?

A

Medium fine (siltstone)
Fine (mudstone)
Very-fine (claystone)

42
Q

How can medium-grain siliclastic rock arenite be futher split?

A

based on the nature of its fragments

43
Q

What are 2 examples of how fragments can split arenite?

There are 4 to choose from

A

Fragment quartz grain- quartz arenite
>25% feldspar- arkose
rock fragment not mineral- lithic arenite
significant muddy matrix- graywacke

44
Q

What is a % abundance chart used for with classification?

A

visually estimating poportion of particular component

45
Q

What is the easiest way to identify different carbonates?

A

all tend to react with hydrochoric acid to varying degrees

46
Q

What will a carbonate be like if dominantly calcium carbonate (CaCO3)?

A

limestone

47
Q

What will a carbonate be if dominantly calcium or magnesium carbonate (Ca,Mg)CO3?

A

dolomite

48
Q

What is a rock matrix?

A

the relative finer grained sized sedimentary particles
in between coarse-grained particles

49
Q

What is the matrix of most carbonate rocks made up of?

A

limestone mud particles 4um in size (micrite)

50
Q

What is cement? (carbonates)

A

lithied post deposition
binding material and is precipitated from moving
solutions in the formation

51
Q

What are the crystals of most cement carbonate rocks made up of?

A

Spar (sparite)- CaCO3 crystal

52
Q

What are allochems?

A

grains or clasts within carbonate rocks

53
Q

What are the most imporant type of allochems?

A

Bioclasts
Clasts
Ooids
Oncoids
Peloids

54
Q

What are bioclasts like?

A

fragmentary or whole organisms

55
Q

What are clasts like?

A

interclasts (intraformational)
Lithoclasts (extra clasts?

56
Q

What are Ooids?

A

coated grains with a regular calcareous cortex and a nucleus of varying composition

57
Q

What are oncoids like?

A

coated grains with an irregular calcareous cortex

58
Q

What are peloids like?

A

sand-sized grains of microcrystalline carbonate
Internally structureless (feacal origin)

59
Q

Both created in 1962

What 2 carbonate classification graphs are there?

A

Dunham
Folk (packing and sorting)

60
Q

What can can be done with the matrix and allochem to produce a rock name?

A

Combined
allochem prefixes are listed in descending order of abundance

61
Q

How can bedding/ lamination be classified?

A

Spacing up to 10mm= lamination 10 to >1000mm= bedding

62
Q

How do pyroclastic form?

A

disintegration of magma, as gases are released by decompression and then ejected from a volcanic vent either in air or beneath water

63
Q

What is the most extreme form of pyroclastic?

A

Nuée ardente

64
Q

What is a Nuée ardente?

A

turbulent, fast-moving cloud of hot gas and ash erupted from a volcano.

65
Q

What are epiclasts?

A

Sedimentary rocks from lithic clasts and minerals released by ordinary weathering
processes from pre-existing consolidated rocks

66
Q

What are volcanic epiclasts?

A

volcanic composition from erosion of
volcanoes or ancient volcanic terrains

67
Q

What is a lahar?

A

volcanic mudflow

68
Q

What is Tuff?

A

consolidated volcanic ash

69
Q
A

Introductory field skills-33742 (7 decks)

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